DISLOCATION-CONTROLLED PRECIPITATION OF TIC PARTICLES AND THEIR RESISTANCE TO COARSENING

The formation of TiC precipitates in an austenitic steel has been investigated by transmission electron microscopy. By nucleation at pre-existing dislocation networks high densities of finely dispersed TiC precipitates were created (4-15 nm average particle diameter), while precipitation in a dislocation-free matrix was found to be completely inhibited. TiC precipitation at stacking faults and grain boundaries was found to be also strongly influenced by the dislocations and their interaction with planar defects. Investigation of precipitate growth as a function of time and temperature showed that in the range 600-900 degree C the TiC precipitates are extremely stable against coarsening. This result is of great importance for elevated temperature applications of the material. A growth mechanism is proposed which is based on solute sweeping during dislocation recovery and enhancement of local supersaturation of solute due to dislocation reactions.